Control for color television



Dec. 13, 1949 c. E. HUFFMAN CONTROL FOR COLOR TELEVISON 3 Sheets-Sheet l Filed Jan. 5, 1946 G Nk v .BN m w Ww ,Tm Q m G .m. i m wn NNN lNvENTDR Mm y BY//M ATTORNEY De@ 13, 1949 c:Y E. HUFFMAN CONTROL FOR COLOR TELEVISION 3 Sheets-Sheet 2 Filed Jan. 3, 1946 INVENTOR M WM ATTORNEY Dec. 13, 1949 c. E. HUFFMAN CONTROL FOR COLOR TELEVISION 3 Sheets-Sheet 3 Filed Jan. 3, 1946 INVENTOR QL a Y 'if ATTORNEY Patented Dec. `13, 1949 2,490,812 coNraoL Foa conca 'rnaavisIoN charles E. Rudman. Upper Montclair, N. J., as`

signor to Allen B. Du Mont Laboratories, Inc., Passaic, N. J., a corporation of Delaware Application January 3, 194.6, Serial No. 638.800

4 Claims. (Cl. P18-5.4)

`This invention relates to a device for obtainf ing signals for use in color television to control the scanning path so as to confine it within a predetermined pattern.

In carrying out the invention, light from the image or screen is used in producing signals which cause the scanning spot to follow its intended path in the pattern so that the colors at the receiver correspond to those that are being picked up at the transmitter.

It is known that color television pictures can be obtained without the use of moving color nlters by use of a screen in which each picture line is divided into primary color lines and grouping these lines side by side in regular order and then scanning the individual color lines separately either in iield groups of common color lines or by scanning lines of dierent colors in sequence.

A screen of this sort can be made by coating a surface with fluorescent material which emits white light or light including the desired primary colors uniformly over its entire area andhaving closely adjacent thereto on the viewed With a screen having the desired characteristics as indicated above, there is the problem of insuring that the scanning spot traverses the proper color line and is not displaced therefrom by voltage fluctuations, or by some other disturbance.

With the present invention signals are obtained by means of photosensitive elements which may be used to control the path of the scanning of a television image. These signals may be used as the deilecting means or they may be used to supplement other deflecting means. The scanning spot is promptly returned to` its proper path after any deviation therefrom. These signals are obtained from photosensitive elements that are illuminated by the image or a projection thereof.

The entire scanned area may be used to provide these signals or a small portion of the end of each scanning line may be used for a control varea separate from the picture image.

In the latter instance a set of photo-sensitive elements are used to develop a signal at the end of each horizontal line, which when applied to the deection system of the television tube or other image reproducing means as de scribed in my application, Serial No. 638,799, filed of even date herewith. corrects for deviation from the proper scanning paths.

The photo-sensitive elements are illustrated as cells and will be referred to herein as cells. although photo tubes, barrier layer cells or other suitable light responsive elements may be used. Load impedances or resistors may be placed in both the anode and. cathode leads of .the photosensitive elements or a single impedance or resistance may be placed in the cathode or anode circuit and a phase-inverting stage used to vobtain polarity reversed from that directly obtained from the load impedance. Only one cell per color is required although a pair of cells may be used for each color when the full output from each cell is desired without the use of a phase-inverting stage.

The invention may be understood from the description in connection with the accompanying drawings in which:

Fig. 1 is a diagram showing an illustrative embodiment of the device;

Fig. la is a diagram showing a modification of a portion of Fig. 1;

Fig. 2 is' a view of that portion of a scree which is used as the control area;

Fig. 3 is a front view of that portion ofthe screen on an enlarged scale and partly broken away;

Fig. 4 is a perspective view of a striated screen having lines of material which emit light of different colors, with photocells in front of the screen;

Fig. 5 is a similar view of a homogeneous nuorescent screen with a striated color lter in front of i Fig. 6 is a similar view showing the image of the screen shown in Fig. 4 projected upon an auxiliary screen with photocells disposed before the cathode-ray tube.

Fig. 'l is the same as Fig. 6 except that the photocells are disposed in front of the auxiliary screen.

Fig. 8 the same as Fig. 6 except that the lcathode-ray `tube screen is made up of homoshown in Fig. 8 and the image is projected upon an auxiliary screen with a color filter close to a cathode-ray tube screen, with photocells disposed before the lter.

Fig. 10 is a perspective view showing a cathoderay tube having a homogeneous screen with its image projected upon an auxiliary screen which has a striated color filter incorporated in it with photocells disposed before said auxiliary screen.

Fig. 1l is a schematic view showing several paths of a scanning spot through a control area and the signals generated thereby.

In the drawings corresponding parts are provided with the same reference characters. Reference characters are provided with subscripts which identify the respective figures in which they occur.

In the drawings reference character I indicates a television receiver using a cathode-ray tube of a television receiver having the usual vertical deflection means 2 and the horizontal deiiectlon means 3. These deilecting means may be either coils or plates.

In this embodiment of the invention the image is indicated as being on the screen 4 of fluorescent material which is applied to or associated with the tube I.-' This screen in a three color system may consist of groups of red, blue and green colored lines R, B and G. In the control area 5 at one side of the screen 4 red, blue and green fluorescent lines R', B' andG' are provided which are continuation of the picture portion of the screen 4.

The portions following phototubes of 8, 'l and 3, or phototubes 6a, 1a and la, represented by block I0, indicate equipment described in detail in my application, Serial No. 638,799, filed of even date` herewith.

As stated in the above mentioned application, the integrating circuit shown therein is adapted to deliver signals to the cathode-ray tube deflection system in which the intelligence derived from part of a line yin a control area is extended to affect substantially an entire line or more.

In this way a small part of a line is used to correctly locate the whole line. The control area 4 The voltages at TI-TI (Fig. 1) as shown In FIg. 11 are as follows:

vTI is negative signal when red light is emitted by 4light is emitted T5 is positive signal when blue light is emitted by at the end of the line may be modulated to maxJ imum or a definite light intensity regardless of picture content of that line and provides for maintenance of the line in proper relation whether the picture contains any component of the color being scanned or not.

During the operation of this device in a three color system, signals are produced across load resistors I2-II in the following manner. When lines R' emit light the red illter IB transmits red light to cell 6 causing it to conduct current from battery 9 through resistances I2, and I3 back to the battery. In like manner, blue light from lines B transmited through lter I3 causes cell I to conduct current from battery 9 through resistances I4 and I5, and in like manner green light from lines G' transmitted by filter 20 causes cell 3 to conduct current from battery 9 through resistances I6 and Il. The voltage drop developed across these resistors provides signals which are applied to the deilection system of cathode-ray tube I through equipment represented by block I0 as described in my application, Serial No. 638,799, led herewith.

Fig. 11 illustrates several possible conditions =of the scanning spot and the resulting voltages at the output terminals TI-TB, Fig. 1, with respect to ground. The voltage of battery 9 is separated from these output voltages byl condensers CI-CB.

screen I. T6 is positive signal when green light is emitted by screen l.

As shown in Fig. 1, three photo-sensitive elements I8, Il and 20 are used in a three color system. Element Il is sensitive substantially to red light only, element I3 is sensitive to blue iight only and element 20 to green light only. It is well understood however that photoelements that are not inherently color selective may be used in cooperation with color filters for the same purpose.

These photoelements may be shielded and hooded to exclude extraneous light and electrical disturbances. When desired they may be located to one side of the screen area i and light may be directed to them by a mirror or optical system, so located and of such a size as not to obstruct view of the picture area of the screen 4.

As the scanning of a complete frame or eld of the screen 4 progresses a series of short bright parallel lines is produced in the control area l. Light from this `area falls on the photoelements Il, Il and 20. When the beam is being deflected at the proper rate, the short lines are all of one color, namely, that of the i'leld being scanned at the moment. and because of the nature of these photoelements or because of the selective filters V.before these photoelements, only the photoelearea 5 (Fig. 3) on an enlarged scale. When the I spot is tracing only one line, say the red line II. both a positive and a negative signal R+ and R are produced as shown in Fig. 11 and no pulse is applied to the block III as explained in my application illed herewith.

When the spot becomes displaced and begins to scan a green line as shown at I4' as it begins' to get oi of a red line I5' the signals R+ and R'- are produced which do not apply a pulse to block III, but the signal G- produced by the green line causes the spot to return to its proper -trace as explained in said application.

Similarly the spot is returned by the signal B"| when it begins to scan a blue line B".

In the modication shown in Fig. 4 the screen is made of striated lines of red, blue and green fluorescent material R4, B4 and G4 from which signals are obtained by phototubes R. B and G for scanning spot control as described above.

In the modification shown in Fig. 5 a homogeneous iluorescent screen S5 is provided with a striated color lter F made up of red, blue and green color strips R5, B5 and Gs for obtaining the different color lines.

In the modiilcation shown in Fig. 6 the image to be viewed is projected upon an auxiliary screen S6 with the photocells located so as to intercept light from the cathode-ray tube screen.

The modiilcation shown in Fig. 7 is similar to Fig. 6 but the cells are located in front of an auxiliary screen S1 onto which the image is projected.

The modication shown in Fig. 8 is similar to -Fig. 6 except that the cathode-ray tube screen is made up of homogeneous color emitting screen material with a striated lter before it and with photocells located so as to intercept light from the striated lter Fs.

The modicatlon shown in Fig. 9 is the same as Fig. 8 except that the cells intercept light from an auxiliary screen S9.

In the modification shown in Fig. 10 the light from a homogeneous screen Sio is projected by lens system PIU onto an auxiliary screen ASw that is provided with color illters or lines of color separating elements through which the light reaches the phototubes 6, 1 and 8 and is used for keeping the scamiing spot aligned as described above.

Figs. 1 to 5 show how this invention can be practiced when images are to be viewed directly on cathode-ray tubes and Figs. 6 to 10 show how the invention can be practiced when images are to be projected optically upon an auxiliary screen.

What is claimed is:

1. In a scanning system for use in color television, a cathode-ray tube having on the inside face thereof groups of parallel lines of screen material in sequence, each line in a group fluorescing in a color different from those of the other lines in said group, short lines of screen material aligned with said parallel lines at one end thereof to provide a signal producing area, the beam of said cathode-ray tube being modulated to a definite intensity while traversing said signal producing area, light illters located in front of said area which pass red, blue and green light respectively. phototubes located in position to receive light from the respective lters and produce control signals for the beam of said cathode-ray tube, and means to apply said control signals to Ehe beam deflectlng system of said cathode-ray ube.

2. In a scanning system for use in color television, a cathode-ray tube having on the inside face thereof groups of parallel lines of screen material in sequence, each line ln a group fluorescing in a color diierent from those of the other lines in said group, short lines of screen material aligned with said parallel lines at one end thereof to provide a signal `producing area, the beam of said cathode-ray tube being modulated to a definite intensity while traversing said signal producing area. light illters located in front of said area which pass red, blue and green light, respectively, phototubes located in position to receive light from the respective filters and produce control signals for the beam of said cathode-ray tube, and means comprising a source of potential and resistors between said source and said phototubes to apply said control signals to the beam defiecting system of said cathode-ray tube.

3. The system of claim 1 in which adjacent lines of said short lines emit light of different colors.

4. The system of claim 1 in which light of different color is emitted from adjacent lines of said short lines directly to said light lters.

CHARLES E. HUFFMAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,415,059 Zworykin Jan. 28, 1947 FOREIGN PATENTS Number Country Date 524,443 Great Britain Aug. 7, 1940 

